VP8 Set Active and ROI Maps

This is an example demonstrating how to control the VP8
encoder’s ROI and Active maps.

ROI (Reigon of Interest) maps are a way for the application to
assign each macroblock in the image to a region, and then set
quantizer and filtering parameters on that image.

Active maps are a way for the application to specify on a
macroblock-by-macroblock basis whether there is any activity in
that macroblock.

Configuration

An ROI map is set on frame 22. If the width of the image in
macroblocks is evenly divisble by 4, then the output will appear to
have distinct columns, where the quantizer, loopfilter, and static
threshold differ from column to column.

An active map is set on frame 33. If the width of the image in
macroblocks is evenly divisble by 4, then the output will appear to
have distinct columns, where one column will have motion and the
next will not.